The present invention relates to a method for growing a thin layer of III-V compound semiconductors on a GaAs substrate, and more particularly to a method for growing, on a GaAs substrate, a thin InGaAs or InAlAs layer with heavy lattice mismatching in two dimensions by a MOCVD (Metal Organic Chemical Vapor Deposition) process.
Currently, optical signals with a wavelength of 1.55 .mu.m are used to process a fundamental signal in high speed data communication networks. As a thin film structure of an optical device, there are multiple thin layers of lattice matching, such as InGaAsP/InGaAs formed on an InP substrate. It is known that recently published multiple thin layers consisting of InAlGaAs/InGaAs have good optical properties, so one takes an interest in such thin layers. A demand for the development of a new device for processing a high speed, large capacity signal is ever increasing. For this, it is necessary to integrate optical and electronic devices and develop a new thin layer material and an optical fiber. In particular, with an increases in a use range, a multiple thin layer structure having a variety of energy band gaps in an active layer of a device is needed.
A technique for growing on a GaAs substrate multiple thin layers of heavy lattice mismatching, such as InAlAs or InGaAs, can freely adjust the energy band gap according to variation of an In composition. However, this technique has disadvantages such as the occurrence of high density dislocation due to the lattice mismatching, three-dimensional thin layer growth due to strain in an initial process for thin layer growth, and the like.
To overcome these shortcomings, a grading technique of the In composition has proposed. Refer to "Strain relaxation of compositionally graded In.sub.x Ga.sub.1-x As buffer layers for modulation-doped In.sub.0.3 Ga.sub.0.7 As/In.sub.0.29 Al.sub.0.71 As heterostructures", J. C. P. Chang, Jianhui Chen, J. M. Fernandes, H. H. Wieder, and K. L. Kavanagh, Appl. Phys. Lett., 60, 1129(1992), and "Surfactant-mediated molecular-beam epitaxy of highly-strained III-V semiconductor heterostructures", E. Tournie, K. H. Ploog, N, Grandjean and J. Massies, Proc. of 6th Int. Conf. on Indium Phoshide and Related Materials Mar., 1994, p49.
In these techniques, a rapid variation in the strain can be minimized by gradually increasing the In composition during the thin layer growth, and the thin layer having the good surface can be grown by reducing the dislocation density. However, since stresses remain within the thin layer and a grading buffer layer becomes thick, it is difficult to apply these techniques to device fabrication.